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MITRE
Adaptive SpectrumUtilization with Software
Defined RadiosDr. Daniel Schaefer 703-883-3664 •
dschaefe@mitre.orgMr. Steve Cox 703-883-6269 •
scox@mitre.orgThe MITRE Corporation
October 2, 2002
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MITRE © 2002, The MITRE Corporation
AgendalProject Overview
- What is it?- Key components and technology used
lWhat Capabilities and Resources were developed- Spectrum and Research community
lTechnology Transfer to Real World Applications
lOngoing Research & Development Opportunities
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Approach: Adaptive System Operation
Radio Frequency (MHz)
Not all spectrum used 100% of time
See what’s free
Spectrum Picture at T1
Occupied SpectrumOccupied Spectrum
Create waveform touse free spectrum
Multiple Componentsto waveform
• form of disjoint OFDM
Transmit Waveform
Monitor channels &repeat processwhen environmentchanges
Waveform compatible with existing spectrum channelization plans and scalableto support wide range of user data rates using non-contiguous spectrum
Waveform compatible with existing spectrum channelization plans and scalableto support wide range of user data rates using non-contiguous spectrum
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MITRE © 2002, The MITRE Corporation
Implementation Considerations•What frequencies to use ???•What’s available ?•Don’t Interfere with others
What frequency do I listen on ???
Coordination & Control
Connectivity !!
How do I connect ???
Adaptive Radio
Implementation Needs• Not interfere with primary users• Close the RF links• Coordinate frequency innetwork - no dedicated controlchannels• Connect all network users• Must share spectrum picturesamong users (Hidden Tx & Rx Solutions)
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What’s Differentl Many sharing applications use compatible waveforms to
simultaneously share spectrum- Overlays such as spread spectrum- Avoidance by proper frequency selection- simultaneous operation limits performance of all systems
l Adaptive Spectrum concept shares spectrum in both time andfrequency
- minimize interference to primary users- allow higher transmit energy using transmit burst
operation avoiding other primary users.
Time Frequency
Tx Spectrum
Tx-3Tx-1 Tx-2
Transmit Packets TransmitWaveform
packet
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Potential Advantagesl Technology provides opportunity for secondary sharing of
frequency channels with both cooperative and uncooperativeusers
l Use of smart protocols internal to radio minimizes the needfor spectrum assignment pre-planning
- Reduced spectrum related mission preplanning- Increased abilities to rapidly adapt to changing missions
l Technology and protocol implementations are hierarchical instructure
- Totally automatic with no dedicated control channels- Dedicated control channel infrastructures for more
positive regulationl for range use can employ additional scheduling
- Distributed control architectures to accommodate uniquemission needs
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Adaptive Spectrum Communication SystemRF Processing
Diplexer orT/R switch
Synthesizer
PreselectFilter
LNA Filter Gain A/D
PA Gain Filter D/AFilterTxFilter
12 - bits
14 - bits
100 MHz
100 MHz
BandbandProcessor
AGC
Transmit Power Control
Frequency
Operating Band RF ProcessingDetermines
Frequency Band ProcessesSub-channels
Analog Digital
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Adaptive Spectrum MOIEDevelopment Environment
Block RFUpconverter
Block RFDownconverter
RF Signals
D/A, digital UpconvertBoard
Quad DSP ProcessorBoard
A/D, digital DownConvert Board
Interface Board
DSP Hardware Platform
Ethernet
Software Tools• TI Code Composer• Pentek DSP tool set
Includes FPGA’s, DSPs,& Configurable ASICS
MOIE has TWO Complete Platforms
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Adaptive Spectrum Use Measurements
Reston BuildingWest Whip Antenna
HP 8591ESpectrum Analyzer
Laptop with LabViewprogram records snapshotsof spectrum use
Workstation withMATLAB analyzes spectrum use
GPIB bus
•Need high time resolution, long term data to determine adaptive systemperformance potentials ~ 1 sec with spectrum analyzer
•Must develop occupancy statistics to optimally design adaptive systemperformance requirements
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l Variation on Orthogonal Frequency Division Multiplex
- Note: Standard OFDM gives gives contiguous set of subcarriers
- MOIE NEEDS ARBITRARY SETS OF NON_CONTIGOUS Transmit Carriers
l NEW Signal Processing Implementation Approaches
- Extensive wave shaping for out-of-band rejection and non-contiguouscarrier implementation
Adaptive Waveform Generation
-250e+3
-250e+3
0
0
250e+3
250e+3
-80
-100
-120
-140
-160
Mag
in d
B
Frequency in Hz (dF = 29.3 Hz)
Conventional OFDMprofile
MOIEImplementation
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Adaptive Waveform Demonstration
SpectrumAnalyzer
Test SignalSource
Optional SingleFreq Tx
SpectrumEstimator
AdaptiveSystem
Controller
Transmitter /Modulator
ReceiveSubsystem
Tx/Rx Chassis Assy
Combined Rx spectrumenvironment
Rx Subsystem in final implementation
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Test Signal Sourcel Test Source represents
assigned user’s signalactivity within afrequency band
l Signal bandwidths aremultiples of thespectrum channelband plan
l Duration and specificchannel combinationsare selected on apseudo random basis
SignalPower(dB)
Frequency (MHz)Note: incremental changes are inkHz increments corresponding toindividual channel assignments
Activesignal
InactiveActivechannel (s)
Click to run movie
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MITRE © 2002, The MITRE Corporation
Adaptive Waveform with Test Signal
l Adaptivewaveform andtest signalsuperimposed
l Lower power signal
is test signal
l Higher power signal
is adaptive
waveform
transmission
l Adaptation rateis reduced forviewing onspectrumanalyzer
SignalPower(dB)
Frequency (MHz)Note: incremental changes are in kHz incrementscorresponding to individual channel assignments
Adaptivewaveformsignal
Testsignal
Click to run movie
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System Demonstration Goal
l Complete End-to-End System Demonstration- Two independent radio sets- Channel and traffic simulator
Adaptive Radio Transmit/Receive
Pair 1 (DSP Chassis -1)
Adaptive Radio Transmit/Receive
Pair 2(DSP Chassis -2)
Traffic Simulator
Traffic Simulator
Channel Simulation
Rx-2
Tx-2
Tx-1
Rx-1
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Generic Application Scenario Example
Airborne Collector
Surface Sensor
Non-CooperativeInterferers
Non-CooperativeInterferers
“Occupancy”Command
CommandedFrequencies
•Monitors 256 30 KHzfrequency binssimultaneously•Commands surfacesensor to transmit on openfrequencies
MITRE
BACKUPS
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Link Negotiation & Establishment(Point-to-Point Case Illustrated Here)
l Since each node makes an independent, local measurementof the radio spectrum some coordination is required beforecommunication can occur:
- spectrum pictures shared between users- optimum picture sharing dependent on environmentNode #1’s Choice of Channels
(AOFDM approach)
PS
D (a
rb. s
cale
)
frequency (arb. scale)
Common Channel Assignments
PS
D (a
rb. s
cale
)
frequency (arb. scale)
Node #2’s Choice of Channels(AOFDM approach)
PS
D (a
rb. s
cale
)
frequency (arb. scale)
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MITRE © 2002, The MITRE Corporation
Summary of Link Negotiation via anExtended RTS/CTS Process
Generate ERTS
Create Waveform
TX ERTS
Tprop
RX & DecodeCompute Link Vars.
(ECTS assumed)
Create Waveform
TX Data
Tprop
RX & DecodeProcess (N)ACK
Tprop.
RX & Decode
Compute (N)ECTS
Create Waveform
TX (N)ECTS
Tprop
RX & Decode
Compute (N)ACK(if explicit)
Create Waveform
TX (N)ACK
Node BNode A Time(not to scale)
Bounds onAdaptation Rates !• Environment•Implementation
Return
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MITRE © 2002, The MITRE Corporation
Adaptive Spectrum Communication SystemBaseband Processing
Serial toParallelModulatorIFFTCyclic
ExtensionPulse
ShapingSerial BitStream
OFDM Transmitter
0
N-1
::
ComplexData
Channel Assignmentand
Moduation Index
14-bitD/A Complex
Upconverter
0
N-1
::
ReceiveData
Parallelto SerialDeModFFTOFDM
BaudBuffer
OFDM Receiver
ComplexData
::
0
N-1
::
ComplexDown
Converter
Correlators Valid Probe (K) channelsTiming
Frequency
ComplexNCO
ChannelSelection,Correction,
andPower
Monitor/Control
::
ChannelResevation
Transmit Power Control
Channel Assignment&
Moduation Index
A/D data
AGC
K K
FFT output
Channel Quality
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MITRE © 2002, The MITRE Corporation
Pentek Quad Processor Board
l Four TMS320C6701 floating-point DSP’s
- operating at 167 MHz
- 4 GFLOPS performance
- SDRAM
- serial full-duplex ports
- zero-wait sync burst & dualport SRAM
- flash memory
- Data transfer rates up to 400MB/sec
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MITRE © 2002, The MITRE Corporation
Pentek Upconverter Board
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MITRE © 2002, The MITRE Corporation
Pentek Downconverter Board
80 MHzclock rate
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MITRE © 2002, The MITRE Corporation
Additional Enhancements
•Transition work togovernmentprogram activities
•Enhance controlinfrastructure
• Add directionalantennas
• Enhanceconnectivity bynetwork relay
• Model operationalscenarios
Coordination & Control
Connectivity !!
Directionalantennas
NetworkData Forwarding
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